1. Field of the Disclosure
The present invention relates to an organic electro-luminescence device and a method of fabricating the same.
2. Discussion of the Related Art
In recent years, there has been increased use of portable electronic devices such as notebooks and personal mobile devices. These devices include display devices. In order to maximize their per-battery charge lifespan, ideally these display device are constructed using light weight and low power consumption technologies, for example using flat panel displays (FPDs) such as liquid crystal displays (LCD) and organic electro-luminescence devices.
Organic electro-luminescence devices have advantages over other display technologies including, for example, having high brightness, having low operation voltage characteristics, having a high contrast ratio because of being operated as a self luminous type display that spontaneously emits light, capability of being implemented in an ultra-thin display, facilitating the implementation of moving images using a response time of several microseconds (μs), having no limitation in viewing angle, having stability even at low temperatures, and allowing flexible fabrication and design of a driving circuit due to operation at low direct current voltages, for example between 5 to 15 V.
The organic electro-luminescence device may be classified into a passive matrix type or an active matrix type. In the passive matrix type, the device may be configured with a matrix form in which the gate and data lines are crossed with each other, and the gate lines are sequentially driven as time passes to drive each pixel. Thus, to achieve a given instantaneous brightness an amount of power equaling the average brightness multiplied by the number of lines may be required at all time to display the instantaneous brightness.
In an active matrix type uses thin-film transistors used for switching individual pixels on and off, a first electrode coupled to the thin-film transistor may be turned on or off for each sub-pixel unit, and a second electrode facing the first electrode may become a common electrode. Further, a voltage applied to the pixel may be charged at a storage capacitance (CST), and applied until the next frame signal is applied. Thus, in contrast to the passive matrix type, in an active matrix type a pixel may be continuously driven for one frame regardless of the number of gate lines. As a result, the same brightness can be obtained even if a comparatively lower current is applied. This has the advantage of providing a low power consumption even in a large screen sized display. In recent years, active matrix type organic electro-luminescence devices have been increasingly widely used for at least this reason.
FIG. 1 is a circuit diagram illustrating one pixel of a typical active matrix type organic electro-luminescence device. Referring to FIG. 1, one pixel of the active matrix type organic electro-luminescence device may include a switching thin-film transistor (STr), a driving thin-film transistor (DTr), a storage capacitor (StgC), and an organic electro-luminescence diode (D). A gate line (GL) may be formed in a first direction, and a data line (DL) may be formed in a second direction crossed with the first direction to form a pixel area (P), and a power line (PL) separated from the data line (DL) may be formed to apply a power voltage.
A switching thin-film transistor (STr) and a driving thin-film transistor (DTr) electrically coupled to the switching thin-film transistor (STr) may be formed at a portion where the data line (DL) and gate line (GL) intersect. A first electrode which is a terminal of the organic electro-luminescence diode (D) may be coupled to a drain electrode of the driving thin-film transistor (DTr), and a second electrode which is the other terminal thereof may be coupled to the power line (PL). Here, the power line (PL) may transfer a power voltage to the organic electro-luminescence diode (D). Also, a storage capacitor (StgC) may be formed between the gate electrode and the source electrode of the driving thin-film transistor (DTr).
When a signal is applied via the gate line (GL), the switching thin-film transistor (STr) is turned on, and a signal of the data line (DL) is transferred to a gate electrode of the driving thin-film transistor (DTr) to turn on the driving thin-film transistor (DTr), thereby emitting light through the organic electro-luminescence diode (D). At this time, when the driving thin-film transistor (DTr) enters an ON state, the level of a current flowing through the organic electro-luminescence diode (D) from the power line (PL) is determined, thereby determining a gray scale. The storage capacitor (StgC) may perform the role of constantly maintaining a gate voltage of the driving thin-film transistor (DTr) when the switching thin-film transistor (STr) is turned off, thereby constantly maintaining the level of the current flowing through the organic electro-luminescence diode (D) until the next frame, even if the switching thin-film transistor (STr) enters an OFF state before then. The organic electro-luminescence device performing such a driving operation may be classified into a top emission type and a bottom emission type.
FIG. 2 is a plan view illustrating a top emission type organic electro-luminescence device, and FIG. 3 is a cross-sectional view illustrating one pixel area including a driving thin-film transistor of the top emission type organic electro-luminescence device, as a cross-sectional view of an “A” portion of FIG. 2. Referring to FIGS. 2 and 3, a first and a second substrate 10, 70 are disposed to face each other, and an edge portion of the first and the second substrate 10, 70 is sealed by a seal pattern 80.
The driving thin-film transistor (DTr) is formed for each pixel area (P) and a first electrode 34 coupled to each driving thin-film transistors (DTr) via a contact hole 32 is formed at an upper portion of the first substrate 10, and an organic emitting layer 38 coupled to the driving thin-film transistor (DTr) and containing light-emitting materials corresponding to red, green and blue colors is formed at an upper portion of the first electrode 34, and a second electrode 42 is formed at a front surface of the upper portion of the organic emitting layer 38.
The first and the second electrode 34, 42 perform the role of applying a voltage to the organic emitting layer 38. A first auxiliary electrode 31 applies a voltage to the second electrode 42. The first auxiliary electrode 31 is formed at the same layer as the driving thin-film transistor (DTr). A second auxiliary electrode 36 is coupled to the first auxiliary electrode 31 via a contact hole 32. The second auxiliary electrode is formed at the same layer as the first electrode 34. Accordingly, the second electrode 42 receives a voltage via the first auxiliary electrode 31 and second auxiliary electrode 36.
Here, the second electrode 42 may be formed of a metal, particularly, with a thin thickness, for example, a thickness of less than 100 Å, to have a semi-transmissive property. If the second electrode 42 is formed with a low thickness, then a sheet resistance increases, and as a consequence the second electrode 42 receives a voltage via the second auxiliary electrode 36 and the first auxiliary electrode 31 formed at the outside of the panel, thereby causing a voltage drop as a result of the distance difference (and consequent resistance) between an edge region of the panel and a central portion. As a result, a brightness difference may be created between an edge region of the panel and a central portion thereof. This causes the image produced by the device to appear nonuniform with respect to brightness across the entire device.